Diaphragm especially for the reproduction of sound



April 1931- R. GOLDSCHMIDT 1,799,162

DIAP HRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Filed May 22 1928 3Sheets-Sheet 1 April 7, 1931. R. GOLDSCHMIDT 1,799,162

DIAPHRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Filed May 22 192 3Sheets-Sheet 2 April 1931- R. GOLDSCHMIDT 1 1,799,162

DIAPHRAGM ESPECIALLY FOR THE REPRODUCTION OF SOUND Filed May 22 1923 3Sheets-Sheet 3 NVSS Patented Apr. 7, 1931 UNITED STATES PATENT OFFICERUDOLF GOLDSCH MIDT, OF BERLIN, GERMANY DIAPHRAGM ESPECIALLY FOR THEREPRODUCTION OF SOUND Application flled May 22, 1928, Serial No.279,740, and in Germany September 1, 1927.

This invention relates to an im roved diaphragm especiall for the repronotion of sound. The fo lowing description is based chiefly on theexample of an electrob magnetic telephone equipped with the improveddiaphragm, but the latter may be equally advantageously applied to anyother sound reproducing machine, for instance to an electro-statictelephone, a loudspeaker and W a phonograph as well asa regulating, measuring, and any other device, where power is transmitted through themedium of a diaphragm.

One object of this invention is to increase the elasticity of a givendiaphragm.

Another equally important ob 'ect is to give a bend and a considerableradius of curvature to the otherwise only slightly curved practicallystraight, characteristic curve of elasticity which determines thedeflection of the diaphragm under different loads or pulls.

These results are attained by means of certain stresses createdartificially in the material of the diaphragm, so asto bring it more orless close to a state of balance (pseudo-astatic e'uilibrium). v

In order that t e invention may be more clearly understood reference ishereinafter made to the accompanying drawings wherein Figure 1 is a planview of my improved diaphragm; Fig. 2 shows aisectional view of theimproved diaphragm shown in Fig. 1

Figs. 3, 4 and 5, are diagrams graphically illustrating the effect ofimprovements in accordance with my invention;

Figs. 6 and 7 illustrate steps employed in the method of producing theuseful stresses in thedia hragm of my invention;

Fi 8 s ows'the form which the im roved diap ragm of Fig. 10 assumesunder t e pull of an actuating magnet system;

Fig. 9 illustrates the section of a diaphragm under the pull of themagnet system, 45 the dimensions bein the same as that of Fig.

8, but without the improvements according to my invention;

Figs. 10,11,12 and 13 are modifications of the method for producing animproved diaphragm; and

taking 8 in Fig. 7, is annihilated entirely, or to a large extent, bybending it into the form 1, Fig. 2, the depth of the bowl being reducedfrom f to This counter-operation, which, for the sa e of reference, maybe called the stretching is to be more or less of a nature such that thediaphragm, after havin been stretched into an almost entirely fiat orm 1or beyond this and held back in the new posia tion, retains sometendency to return towards its fornier shape 8 through latent elasticstresses.

The stresses are spread over the whole dia- V phragm, practically everysquare millimeter part in the vaulting and stretching. The efi'ect ofthis preparationis that the diaphragm is made to resist a strongmagnetic pull and to adapt its characteristic tot at of the magnet, themeaning of which will be explained with reference to Figs. 3, 4 and 5.

In-diagram Fig. 3, P is the pull upon a diaphragm vertical to its plane,and D is the corresponding deflection. Character I refers to an ordinarydiaphragm. If the latter is prepared as described above thecharacteristic changesto curve II in Fig. 3 or assumes the unsymmetricalsha c Fig. 4.v The characteristic can be shape atiwill and dependsentirely upon the vaulting and stretching process.

' For the adaption of the characteristic of the diaphragm to a givenpurpose, the electro-ma netic tele hone is a good example. I

The pu 1 exercise by the permanent magnet u on the diaphragm de ends ontheir relative distance, a relation in icated by the characteristic ofthe magnet, curve III in Fig. 5. If the distance is zero the pull is 0A.If there was no magnetic pull it all, tho position zero or at leastextremal;

of the diaphra would be at C. The dis-' tance 00 must such that, if thediaphragm is deflected until it touches the magnet, its elastic force OBexceeds the attractive force OA of the magnet by an amount of safety AB,so that the diaphragm cannot stick to the magnet. An ordinary diaphragmwith a strai ht characterimic (IV in Fig. 5) would efle'ct into positionF (distanoe OF), a ,1 point where the magnetic and elastic forces areequal. The position which an improved characteristic (curve V) wouldassume in'the magnetic field, would correspond to the point ofintersection G (distance OG) of the curves III and Y. The angle ofintersection ought to be very near acute. The charmay be so loselyacteristic of elasticity Tadapted or assimilated to the characteristicIII of the m etic force that through the differential action of bothforces in the areanear -G the resultant elasticity of the diaphragmbecomes almost infinite. The diaetic phragm practically floats in the mafield, this result being achieved under t e espronounce'd curvature ofits characteristicthere is no danger of the diaphragm sticking to the maet. Extreme'elasticity is combined with stability. Naturally thediaphragm connot be quite astatic over a wide range, but is very closeto a state which in steam engineering and physics is calledpseudo-astatic, a term which mi ht be used to designate such a condition0 sensitiveness.

The pseudo-astatic state may be verified by holding the telephone to theear and exercisin a small pressure upon the case of the telep one,thereby-compressing slightly the air enclosed between the tympanum andthe diaphragm and noting the clickin noise due to the extremesensitiveness of the diaphragm upon the slightest change of pressure.

The method of vaultin and stretching may be varied considerab y. Iprefer the mode as illustrated by Figs. 6 and 7. The diaphragm 1 ispressed (vaulted) into the form. Fig. 6 and afterwards by pres re frombelow asindicated by the arrows, tra sfor-med (stretched) into that ofFig. 'l. The bevelhng (9) of the diaphragm along its circumference (likea mirror) is important. It

gives way and adapts itself automatically and permanently to the shapeof the diaphragm, when the latter undergoes its transformation. Thishelps to secure the bending momentums and is essential in producingdin.- phragms with practically equal properties.

t forms a buffer between the frame or rim and the diaphragm proper, thusprotecting the latter against natural as well as accidental changes.

The unsymmetrical shape Fig. 4, which is very useful in electromagnetictelephones, is

obtained by stretching the diaphragm so that it bulges but somewhatbeyond the flat form a1 measurements. Fig. 8 refers to a diaphragm inaccordance with this invention, assuming the shape. X under theinfluence of the magnet. This shape changes to Y, if a small directcurrent is passedthrough the telephone coils upon the magnet. For anordinary diaphragm with the identical general dimensions but without theartificial stresses the corresponding forms are those of F ig. 9. Figs.8 and 9 are directly comparable, the

cross-hatched areas illustrating the larger volume of air displacedunder influence of the same current by the diaphragm Fig. 8 inaccordance with this invention.

Figs. 10-13 illustrate a mode of stretching carried'out at the same timeas the diaphragm 1) is'insered into its frame (2), the

vaulting having been done beforehand.

The permanent maintenance of the stresses in the diaphragm is offundamental importance. Before providing proper means ,to se- 1curethem, I have had the experience that a number of. originallyexcellent diaphragms had become perfectly useless within 24 hours,others within a week. One ofthe protecting means is the bevelling (Fig.7). Others are indicated in Figs. 1,2,6 and 8, where the diaphragm issecured in a strong frame by corrugating the rim during, the process offixing it in the frame.

In order to guard against extension and contraction through theinfluence of temperature changes, the material of the frame ought to bechosen so that ithas practically the same coeflicient of extension asthat of the diaphragm itself. An iron diaphragm ought to have an iron.frame, if possible. If, however, the latter .is firmly screwed againsta different material, a bi-metallic action may again make the diaphragmalive to the temperature of its' surroundings, destroying its qualitiesthrough warping. This influence has been borne out my early experimentswith a telephone equipped with the new diaphragm, the latter becominguseful only after warming it up by holding the tele-.

phoneto the ear for several minutes.

To make the diaphragm independent of its neighbourhood flexibleinsertions (10) Figs. 14-15, for instance paper or rubber rings areprovided which insulate the diaphragm mechanically.

If such insertions are'made very flexible and the shape of the diaphragmand its rim such that it becomes in itself resistant against alterationof the interior stresses, the frame (2) may be reduced to plain ringswhich are pressed against the rim (11) provided that the metal is nottoo thin.

With a very thin diaphragm of large diameter, however, it is necessary,not only to insert it securely, into a strong frame, but to doso beforethe vaulting or anyway before the stretching operation is carried out,as otherwise there is a chance that the diaphragm has become anabsolutely different one, after having been placed into the apparatus ofwhich it forms a part.

Claims:

1. The method of creating artificial stresses in a diaphragm whichconsists in forming the diaphragm into a vaulted shape and subsequentlyapplying permanently bending forces to the diaphragm in the directionfrom the convex to the concave side of the original vaulting forshifting said diaphragm in a direction opposite to the vaulted positlonthereof.

2. The method of creating artificial stresses in a diaphragm upon whicha perm'anent pull is exercised which comprises forcin the material ofthe diaphragm into a vaulte shape and thereafter deforming saiddiaphragm to a position wherein the combined action of the external andinternal forces are such that the diaphragm operates near a point offiexure of its characteristic curve.

3. A sound reproducing diaphragm comprising a sheet of material which issubjected to artificial stresses, a clamping device, the rim of saiddiaphragm being rigidly secured in said clampingdevice, said diaphragmhaving an annular beveled portion pressed therein intermediate theclamped portion and-the central portion thereof, said central P01131011having the material thereof compressed for establishing permanentinternal forces in said diaphragm.

4. A diaphragm comprising a sheet of magnetic material, a clampingdevice for securlng a rim portion of said diaphragm at its periphery,said diaphragm having a central portion and an annular bevelled ortionpressed therein intermediate the o amped 'portion and said central(portion, said cen tral portion being stampe with dies having the shapesof continuous curves first in one direction and then in the oppositedirection, and said central portion having the material thereofcompressed for establishing permanent internal forces in said diaphragm.

5. A sound re roducing diaphragm comprising a sheet 0 material having anannular rimportionand a central portion, said annular rim portion beingfixed in a retaining restoring saidv diaphragm to a position ;ap-

proximating the original position of the diaphragm with internal forcesestablished therein and maintained by said retaining frame.

6. The method of forming a sound reproducing diaphragm which consists inapplying forces to the diaphragm to press the dlaphra'gm into an archedshape and subsequently applying forces to the diaphragm in the oppositedirection to flatten the arched sha e diaphragm into a substantiallyplane sur ace for establishing permanent internal forces within thematerial of the diaphragm.

7. A sound reproducing diaphragm comprising a sheet of material havingan annular rim portion and a central sound reproducing surface, meansfor gripping said sheet of material at its rim portion, said diaphragmbeing vaulted in the central portion thereof in one direction andflattened substantially throughout the vaulted portion by forces appliedin the opposite direction for establishing permanent internal forceswithin the material of the diaphragm.

8. A sound re roducing diaphragm comprising a sheet 0 material having arim portion, means for gripping said rim portion, the central portion ofsaid diaphragm being 'vaulted in shape in one direction and thereafterdeformed from the vaulted shape in the opposite direction to a positionin which the internal structure of said diaphragm is maintained under astate of permanent internal stress.

9. In a sound reproducing diaphragm, a sheet of material having a rimportion and a central portion, a frame for gripping said mm portion,said frame having substantially the same coefficient of expansion underconditions of rising temperature as the materlal of the diaphragm, thecentral portion of said diaphragm being vaulted first in one dlrectionand subsequently deformed in the opposite direction for maintaining saiddiaphragm in a condition of permanent internal stress.

A sound reproducing diaphragm comprising a sheet of material having arim portion and a central portion, a frame structure surrounding saidrim portion, thermal insulation means disposed between said framestructure and said rim portion, said central portion being vaulted firstin one direction and subsequently deformed in the opposite direction tomaintain the internal structure of said diaphragm in a condition ofinternal stress.

11. The method of forming an accoustic diaphragm to be actuated by theforce of an external field which varies at different points in a gap,which consists in vaulting said diaphragm in one direction by stampingwith a curvilinear die, and counter-vaulting by stamping in the oppositedirection in such manner that the restoringforce of said diaphragm isapproximately equal to said external field force over a substantial partof the working portionof said gap. r

12. The method of forming an acoustic stamping with a curvilinear die,and countervaulting by stamping in the opposite direction, in suchmanner that the restoring force of said diaphragm is approximately equalto said external field force over a substantial part of the workingportion of said gap.

14. The method of forming an acoustic diaphragm to be actuated by theforceof an external field which varies atdifierent points in a gap whichconsists in clamping said diahra m in a mountin rin stam in said U 7portion bent from the diaphragm withdie and counter-die to form,

a central arched portiogf,l and an annular rim rection oppositetothedirection of such vaulting, and then applying pressure from theconvex side of said vaulted portion to cause said vaulted portion toassume a substantially flattened form, whereby the restoring force ofsaid diaphragm is approximately equal to the said external field forceover a substantial frequency of an acoustic diaphragm which 3 points ina gap, a mounting frame of a matepart of the working portion of saidgap.

, 15. The method of lowering the resonance consists in vaulting saiddiaphragm by stamp ing with a' curvilinear die, and.counter-vaultpositedirection.

"ing said diaphragm by stamping in the opat position in a diof anexternal field which varies at difierent points'in a gap, a mountingframe in which said diaphragm is clamped, heat insulating piecesinsulating said diaphragm from said frame, said diaphragm being vaultedand counter-vaulted by stamping operations in opposite directionswhereby said diaphragm possesses a restoring force approximately equalto said external field force over a substantial part of the workingportion of said phragm to be actuated by the force of an external fieldwhich varies at diflerent points in a gap, which consists in clampingsaid diaphragm tightly in a mounting frame, andapplying permanentcompressive forces in said diaphragm by vaulting said diaphragm in onedirection by stamping with a curvilinear die, and counter-vaulting bystamping in the opposite direction.

18. The method of forming an acoustic dia- 19. The method of forming anacoustic diaphragm to be actuated by the force of an external fieldwhich varies at different points in a gap which consists in clampingsaid dia phragm in a mounting ring, stamping said diaphragm with die andcounter-die to form a centralarched portion and a frusto-conical annularzone, and then applying pressure .from the convex side of said vaultedportion to cause said-vaulted portion to assume a subta'ntiallyflattened form, whereby the restoring force of said diaphragm isapproximately equal to the said external field force over a substantialpart of the working portion of said gap.

In testimony whereof I afix my signature. RUDOLF GOLDSGHMIDT.

I 16. In an acoustic device,an acoustic diaphragm adapted to be actuatedby the force of an external field which varies at diflerent rial havingthe same temperature-coefficient as said diaphragm in which saiddiaphragm 1 is clamped, said diaphragm being vaulted and counter-yaultedby stamping operations in opposite directions whereby said diaphragmpossesses a restoring force approximately 1 equal to saidexternalfield'force over a substantial part of the working portion ofsaid 17..In a acousticj'device, an acoustic dia- I phragm adapted to beactuated by theforce

